Slip-indicator.



G. A. JOHNSTONB. SLIP INDICATOR.

APPLICATION FILED APILSO, 1908.

Patented Nov. 30, 1909.

I nventor; e A.Johnstonfe,

Geog 5y UNITED STATES PATENT OFFICE.

GEORGE A. JOHNSTONB, OF REVERE, KABSLGHUBETTS, ABBIGNOB '10 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SLIP-DIDIOLTOB.

Speculation of letter: Patent.

Patented Nov. 30, 1909.

Application filed April 80, 1908. Serial llo. 480,072.

To all whom it may concern:

Be it known that I, GEORGE A. Joans'rona, a sub'ect of the King of Great Britain, residm at Revere, county of Essex, State of assachusetts, have invented certain new and useful Improvements in Slip-Indicators, of which the following is a specification.

My invention relates to stroboscopic slip indicators for induction motors and its ob- 'ect is to provide a simple and self-contained indicator easily adjusted to any induction motor for determining its sli and capable of use with different motors aving different numbers of poles.

In carrying out my invention a source of light which varies in bri htness with each cycle of the supply circuit of the motor is periodically exposed to the observer at intervals which vary in frequency with the speed of the motor. The periodic exposure may be secured by screening the source of lig t from the observer by a rotary shutter driven in synchronism with the motor and having an opening which enables the observer to see the source of light only when the shutter is in a predetermined position. If the motor is running without slip the source of light will always be at the same stage of its variation when exposed to the observer and will a pear steady, but if the motor is slippin e successive exposures take place at di erent stages of variation of the light which appears to pass throu 11 its entire range of variation at a rate endent on the amount of slip. The preerred source of light is an electrol tic cell, preferably one having an electro e of an alloy containing aluminum, since such an electrode in an alkaline electrolyte will besome illuminated when an alternating voltags of from one hundred to two hundred volts is applied, the luminosity appearing and disappearing durin each eye e at the aluminum electrode, winch is plmd in a position to register with the opening in the rotatingishutter and is periodically exposed to the 0 server by the rotation of the shutter.

My invention will best be understood in connection with tho accompanyin drawings which are merely illustrative 0. one form in which the invention may be embodied and in which Figure 1 is a plan view of a slip indicator; Fig. 2 is a side view partly in section along the line 2 2 of the device shown in Fig. 1; and Fig. 3 is a. diagrammatic view showing the relation of the electrolytic cell and the rotatin shutter to the supply circuit and the in action motor.

In the form of the device shown in the drawings the variable source of light is an electrolytic cell which comprises a glass vesas] 1 containin an alkaline electrolyte in which the aluminum electrodes 2 and 3 are immersed. The electrode 2 is small and is made of are aluminum to diminish the heating w ile the electrode 3, which is the source of light, is preferably made from an alloy. of aluminum which becomes brightl illuminated duri each cycle, the electrod being made in t e form of a plate and mounted upon a backing or support 3 of any suitable insulating material.

In repairing the cell the electrodes are first tloroughly coated by applying a relatively high voltage for some tune and the face of t e plate electrode 3 is then cleaned of the coating to increase the illumination at normal voltages. The electrode 3 or other source of light is normally concealed from the observer by a movable shutter which is shown in the form of a rotatab e disk 4 mounted in a framework 5 on a shaft 6 driven in any suitable manner in synchronism with the induction motor 7 which, as shown in Fig. 3, is energized from the alternating currentsup 11y circuit 8 across which the electrodes 2 an 3 are connected through a hand switch. The electrolytic cell is referably inclosed in an opaque casin 9 01ming part of the framework 5 and having in one side a series of openings or peep-holes 10, [1 and 12 with which the source of light or disk electrode 3 may be brought into registry. The movable nutrior disk 4 has a small slit or peep hole preferably in the form of a circular opening 13 which comes into registry with tie openin 10 and the source of light at each rcvoution of the disk.

The device above described is adapted for measuring the slip of induction motors and its operation will best he understood in connection with a motor of (he twopole type. The electrode 3 becomes bright and then dm'k during each cycle on tho sup )l circuil H to which it Is vonnmlod uml l'l' tho molor is running without slip the opening 13 in the shutter will 1' giater with the openand alwu s expose the clc ctrodc 3 lo the server at t 1c same stage in its variation in luminosity. If tbeelcctrode is fiist exposed when it is br ght, it will die down-and a 21in become br ght by the time the disk ma es one revolution and again exposes it, and the light will therefore appear steady. If the motor is slipping and the first revolution of the shutter exposes the electrode when it is bright, the next cxposurc will take place later m the cycle, utter the intensity of the illumination on the electrode has begun to diminish, and since this aciion is cumulative he electrode is eventually exposed to the observer at every sta e of its variation in brightness. The length of the interval between each exposure and therefore the extent of chat e m the appearance of the source of hg t since the preceding exposure de ndson the amount of slip, hence the len t1 of time apparently required for thc e ectrodc to complete its cycle of illumination is u measure of the slip of the motor. In practice the determination is made most easily by noting the number of times the electrode appears bright during a definite period of observatiou.

Since the speed of an induction motor varies inversely with the number of pairs of poles, it is necessary to make some provision when the device is used with a motor having more than two poles for exposing by any suitable mechanism the electrode or other source of light with the same freqncncy as in the case of a two ole motor, and where the disk or shutter 4 is driven at the same speed as the motor shaft the electrode is exposed in the four pole motor twice and in a six-pole motor three times during each revolution of the motor shaft. This result may be accom lished by driving the disk at twice the spec of the shaft of a four-pole motor and at three times the speed of the shaft of a six pole motor, but the preferred arrangement is that shown in the drawing in which the disk or shutter is provided with two pcc -holes or openings 14 diametrically 0 posite each other on the circumference o a circle concentric with the axis of the disk 4 and arranged to register with the opening 11 in the casing. and also with three openings or peepholcs if; placed 120 apart on nnolhcr circle concentric with the axis of the disk 4 and arranged to rogistcr with the opening 12 in the casing. The electrode 3 is made adjustable nnd is brought into registry with any one of the openings 10. 11 or 12 by means of a thumb-screw 16, which is attached to the insulating bushing 3" and projrrls through a slot in the framework. lVhou the shutter 4 is directly connected to the shaft of n four-polo induction motor the olcrlrodc is adjusted to conic into ing 10 in the casin registry with the owning l1 and the openings 14, so that the source of light is exposed twice during each revolution of the motor shaft, while with a six-pole motor the clectrodc is placed in front of the opening 12 in registry with the openings 15 and is exposed three (inns during each revolution of the motor shaft.

My invention may be embodied in many other forms than shown and described and I therefore do not wish to be restricted to the exactform shown but intend to cover by the appended claims all changes and modifications within the spirit and scope of my invention.

\Vhat I claim as new and desire to secure by Letters Patent of the United States, is,

1. In a. visual slip indicator for induction motors, the combination with a source of light which varies in intensity in synchromsm with an alternatin current circuit, of means for exposing salt? source of li ht at intervals varying in frequency wit the speed of an induction motor connected to t c alternating current circuit.

2. In a visual slip indicator for induction motors, the combination with asource of light which varies in intensity in synchronism with an alternating current circuit, of a movable shutter actuated by an induction motor connected to the alternatin current circuit and man ed to momentai y expose said source of lifi t at intervals varying in frequency with e speed of the motor.

3. In a visual slip indicator for an induction motor, the combination with a, source of light which varies in intensity in synchronism with an alternating current circuit, of a rotary shutter driven in synchronism with an induction motor connected to the alternating current circuit, said shutter having an openingi for intermittently exposing said source of ght.

4. In a visual slip indicator for induction motors, the combination with a source of light which varies in intensity in synchronism with an alternating current circuit, of means for making during one revolution of an induction motor connected to an alternoting current circuit a series of exposures of said source of light, said exposures being proportional in number to the number of poles of the motor.

5. In a visual slip indicator for induction motors, the combination with a source of light which varies in intensity in synchromsm with an alternating current circuit, of a shutter moved at a rate dependent on the speed of an induction motor connected to an alternating current circuit, said shutter having openings arranged in lmcs equal in number to the various numbers of pairs of poles used in induction motors, the number of openings in each line lining pro mrliunnl to n difl'crent number of mics, and means for varying the relation al said source of light to said lines of openings in said shutter to make during one revolution of the motor a series of exposures of said source of light, said ex ures bein proportional in number to t 1e number 0 poles of said motor.

6. In a visual slip indicator for induction motors, the combination with a source of l' ht which varies in intensity in synchronism with an alternating current circuit, of a rotary shutter rotated in synchromsm with an induction motor connected to the alternating current circuit and having openin arranged in concentric circles with a di erent number of openin in each circle, and means for moving sai source of light and said shutter relatively to each other to bring said source of light into registry with the o enings in any one of said circles.

T. n a visual slip indicator for induction motors, the combination with an electrolytic cell having an electrode which varies in luminosity in synchronism with an alternating current circuit, of means for exposing said electrode at intervals vuryin in frequency with the speed of an induction motor connected to the alternating current circuit. 8. In a visual slip indicator for induction motors, the combination with an electrolytic cell havin an electrode which varies in luminosity m synchronism with an alternating current circuit, of a casing for said cell with an opening for exposing said electrode, a shutter for said opening driven in synchronism with the motor to expose said electrode at intervals varying in frequency with the s eed of said motor.

9. n a visual slip indicator for induction motors, the combination with an electrolytic cell havin an electrode which varies in luminosity 1n synchronism with an alternating current circuit, of a rotary shutter driven in synchroniam with an induction motor connected to the alternating current circuit, said shutter having an openin which intermittently registers with said e ectrode to expose it.

10. In a visual slip indicator for induction motors, the combination with an electrolytic cell having an electrode which varies in luminosity in synchronism with an alternating current circuit, of a rotary shutter driven in synchronism with an induction motor connected to the alternating current circuit, said shutter having openin arranged in concentric circles, and means or moving said electrode and said shutter relatively to each other to bring said electrode into r istry with the openm in an one of said circles.

In witness w iereof, have hereunto set $368 hand this twenty seventh day of April,

GEORGE A. JOHNSTONE.

Witnesses:

JOHN A. MoMnzos, Jr., CHARLES E. Harman. 

